The use of checkweighers to weigh moving objects (e.g., packages) is well known, and various checkweigher designs exist for this purpose. In general, however, a checkweigher may be described as a high-speed weighing device for the in-motion weighing of objects as the objects travel along a conveyor. A checkweigher is typically installed to a conveyor line such that an in-feed conveyor is provided for delivering objects to the checkweigher and a discharge conveyor is provided to transport objects from the checkweigher to a downstream location. The checkweigher itself also typically employs a conveyor to transport objects one at a time across a static scale, which is essentially a vertically deflectable mechanism operable to effect weighing of the moving objects.
All checkweighers, in one form or another, employ a sensor that transforms the weight of an object into a usable signal. Typically, this signal is converted into a readable value by some type of analog-to-digital (A/D) converter. Sensors typically used for this purpose include, for example, strain gauge load cells, electromagnetic force restoration weigh cells, or other sensors such as capacitive or inductive sensors.
Regardless of the specific type, all such sensors will, over time, experience a slight change in characteristics. As a consequence, the output of such a sensor in response to a given load will eventually differ from the output of a freshly calibrated sensor in response to the same load. This is particularly true for sensors that are not highly accurate, such as strain gauge load cells. To a lesser degree, this is also true for more accurate sensors, such as electromagnetic force restoration load cells.
In any case, if the characteristics of a sensor change, the readable weight value produced by the sensor will change as well. Therefore, with respect to a checkweigher that employs such a sensor(s), it may be impossible to differentiate between a change in weight of an object over time and a change in sensor characteristics over time, unless samples of the object in question are intentionally removed from the checkweigher line and independently weighed on a static scale.
Thus, known techniques for validating accurate checkweigher (i.e., weight sensor) operation require operator intervention. Typically, such a validation process requires that an operator stop the conveyor line feeding the checkweigher of interest, collect object samples (or a reference sample) to be weighed, weigh the object samples on a static scale, and then run the object samples multiple times (commonly 15 times or more) over the weighing sensor of the checkweigher to validate the weighing function of the checkweigher.
This technique also requires the operator to manually collect and record the associated weight data—both of which occur offline. This data may be collected and may be further archived for reference purposes and/or used to make adjustments to the weight sensor(s) of a checkweigher of interest. Because this is a manual process, a periodic audit function is typically required to ensure that validation checks are being performed.
An alternative checkweigher validation technique involves sampling a set of objects using a built-in sampling function of a checkweigher of interest. Such a sampling operation may typically occur without stopping the associated conveyor line. Generally, the checkweigher rejects the set of sample objects after they are weighed by the checkweigher during such a sampling operation. After being rejected, the sample set of objects must be collected by an operator and transported to an offline static scale for weighing. The weighing function of the checkweigher is then validated by comparing the weights of the objects as reported by the static scale to the weight of the objects as reported by the checkweigher.
One disadvantage of both of the aforementioned checkweigher validation techniques is that that they both require operator intervention. In the former case, all the steps of the validation process must be initiated and performed by an operator. In the latter technique, all the steps of the validation process must be initiated by an operator, and the operator must still collect the objects after weighing by the checkweigher, transport the objects to an offline static scale and perform the weighing operation. In both cases, the operator must manually collect and record the weight data associated with the offline static weighing operation.
Ultimately, checkweighers must be periodically validated in order to ensure the proper and accurate operation of their weighing function. It is obviously desirable that such validation occurs without any risk of validation process failure. Consequently, it can be understood that a validation system and method that removes the possibility that validation operations may be skipped or performed improperly would also be desirable. Systems and methods of the present invention are useful in this manner.